Humidity sensitive instrument



Aug. 21, 1934. w. c. GOSS HUMIDITY SENSITIVE INSTRUMENT Filed Oct. 19,1931 2 Sheets-Sheet 5 R m J 7 ;7 .7 m E M q m0 M 4a m M 1 mm J \T M ArWm Wm 6 0 w W M B 4 vi 1 l 21, 1934. w. c. GOSS v HUMIDITY SENSITIVEINSTRUMENT Filed Oct. 19, 1951 2 Sheets-Sheet Patented Aug. 21, 1934HUIWIDITY SENSITIVE I NSTRUNIENT Worth 0. Goss, Seattle, Wash.

Application October 19,

' Claims.

This invention relates to humidity sensitive instruments and hasreference in particular to an instrument designed to be functionallyactuated in accordance with changes of relative hui midity of thesurrounding air for the purpose of operating a switch, valve, lever orother device, to cause adjustment or operation of a control mechanismwith which the element may be associated.

It is the principal object of this invention to provide an instrument ofthe above character especially useful for humidity control and which 1will operate with accuracy under all conditions of humidity, which willbe extremely sensitive to changes of relative humidity, and which willoperate quickly, and will maintain its accuracy and efliciencyindefinitely.

It is also an object of the invention to provide a device of the abovestated character that is adapted tovarious uses, that is simple inconstructicn and mode of operation, and which can be manufactured andsold at a small cost.

The objects of the invention reside primarily in the novel arrangementof wooden strips composing the element, especially with reference toannual rings and assembled relationship whereby their degree ofexpansion and contraction is maintained within certain definite limitsto avoid any damaging strains or stresses which might operate to renderthe instrument inaccurate.

In accomplishing these and other objects I have provided the improveddetails of construction, the preferred forms of which are illustrated inthe accompanying drawings, wherein- Figure 1 is a perspective view of ahumidity control device constructed in accordance with the presentinvention.

Figure 2 is a central, vertical section of the same.

. Figure 3 is an enlarged sectional detail lengthwise of the element,particularly illustrating the end grained hygroscopic element and thelongitudinal grained backing strip.

Figure 4 is an enlarged cross section taken on the line 44 in Figure 3.I

Figure 5 illustrates the use compensate .for inaccuracies.

Figure 6 is a perspective view illustrating the manner of cutting thehygroscopic strips from a wooden board to provide a definite percentageof expansion or contraction incident to humidity changes, andillustrating the position of the board within the log before it isremoved therefrom.

of two strips to their thickness, direction of grain, direction of.mounts a contact point 8 with which a circuit 1931, Serial No. 569,830

Figure 7 is a perspective view explanatory to the methods of cutting thestrips.

Explanatory to the invention it will here be stated that in devices ofthis general character the element or elements are made up of two fiatwooden strips, one a hygroscopic facing strip that has an appreciableamount of expansion or contraction incident to changes of relativehumidity, and the other a backing strip that is relativelynon-expandable or non-contractible for changes of humidity; these twostrips being carefully prepared and glued or otherwise suitably fastenedtogether. This element is fixedly mounted at one end with its other endfreely movable for actuating an instrument for controlling or indicatingpurposes. Changes in relative humidity of the surrounding air will causecontraction or expansion of the hygroscopic strip in accordance with thedegree of change and this by reason of its connection with the backingstrip causes a lateral bending of the element in one direction or theother and this movement of the element is employed to actuate a controldevice.

Referring more in detail to the drawings- In Figure 1 of the drawings Ihave shown the present device as employed for the purpose of opening andclosing an electric circuit. The control element proper is mounted on abase plate 1 of electrically non-conductive material. An anchor block 2is fixed rigidly to the upper end of this base plate and has securedtherein the upper ends of the bi-strip elements 3 arranged in tandemseries of four elements each. All of these elements are alike inconstruction and size, and each is fitted at its lower end with a clip4. Pivot rods 5-5 are extended through the alined clips of elements ofeach series and links 66 pivotally connect the ends of one of the rods 5with the ends of the other so that the two series of elements arethereby operatively connected and will move together.

It will be here stated that the above described method of mounting andof connecting the elements is only one of a number of different ways ofconstruction and it is not intended thatit be confined only to themethod described.

Extending downwardly from one of the clips 4 is a flexible or springlikeextension leg 7 and this wire 9, from one side of an electric circuit.connects. A wire 10 from the other side of the circuit connects with asimilar contact point 11 that is mounted on an arm 12 carried by anadjustable lever 13. This lever is supported by a pivot 14 strip,

I of the strip.

fixed in the upper end of the base plate, and the lower end portion ofthelever may be moved laterally in opposite directions to adjust thecontact point 11 toward or from the contact point 8. An arcuate plate 15with graduations thereon is attached to the lower end of the base platebeneath the swinging end of the lever, as a'gauge, for making adjustmentof the latter.

With the device so constructed, a circuit may be closed between thecircuit wires by bringing the contact points 8 and 11 together and itwill be opened when the points are separated. Thus, movement of theelement by reason of changes in relative humidity, as presentlydescribed in detail, will cause a corresponding movement of theextension leg 7, and this may be made to open or close the circuit atany desired condition of humidity by proper setting of the lever 13.

It will be stated here that various kinds of control devices may beemployed in connection with this type of element for opening a switch,for closing a valve, or for doing otherwork, and the presentillustration is merely explanatory to the mode of operation and thevarious uses to which the device may be put.

In the construction of the various elements of the present device, Iemploy a backing strip 16 of longitudinal grained wood, preferablyAlaska cedar or other suitable wood of similar or like properties. As afacing for the backing, I employ a very thin wooden strip 17 preferablyof end grained yew wood, or other suitable wood of similar or likeproperties.

As a matter of explanation, it will here be stated that bylongitudinally grained wood I mean a strip of wood in which the fiberforming the grain of the wood extends lengthwise of the strip. By endgrained wood I mean that the direction of the grain is directly throughthe strip from face toface as distinguished from lengthwise of the oreven crosswise thereof. This would mean that a strip as used for facingwould have the pores opening to the flat inner and outer faces In astrip as used for the backing, the pores would extend lengthwise andwould not be open to atmosphere except at the ends of the strip.

Figure 7 is explanatory to the method of cutting the strips to providethe longitudinal grained" and end grained pieces. In'this figure, Ldesignates a wooden log and at 16a and 16b I have defined stripssuitable for use as backing strips. These strips extend lengthwise ofthe log and therefore the grain of the wood in the strips is lengthwisethereof. Therefore, these are termed longitudinally grained strips. Theflat inner and outer surfaces of the strip 16a are in planessubstantially tangential of the annual rings of the log and thus thisstrip is identified as a "longitudinally grained tangential cut. Thefiat inner and outer surfaces of the strip 16b are radially of the logand therefore this strip is identified as a longitudinally grainedradial out.

At one end of the log I have shown a slab s cut therefrom by cuttingthrough the log in spaced planes perpendicular to its axis and directlythrough the grain. ".his slab is identified as an end grained slab. Cutfrom this slab are end grained strips 17a and 17b. The longitudinaldirection of the strip 17a is substantially tangential to the annualrings 1' of the slab and this strip therefore is identified as atangential end grained cut. The longitudinal direction of the strip 17!)is radial of the slab and the annual rings 1' are. substantiallydirectly across the strip, therefore this strip is identified as a cut.Both strips should be be free of any imperfections. wood is treated,such as by boiling in water or other liquid, or otherwise, to remove allmaterial from its cells so that they will be open for easy penetrationand intimate contact of air with the cell structure. Also, it has beenfound that this treatment straightens out the fibers of wood that arebent over on the surfaces of the strip in the cutting and thus permitseasier penetration of air into the cell structure and pores of thestrip. The strips after proper preparation are secured together by meansof a water free glue.

In order to avoid detrimental case hardening taking place in the elementafter it has been put into use by reason of stretching or compressingthe strips beyond their elastic limits, a very careful selection ofmaterials must be made and due consideration must be given to a certainrequired relationship between the stiffness of the backing strip and thestrength and hygroscopic expansion radial end grained carefullyselected, to Preferably, the yew of the facing strip. The backing stripmust be.

sufiiciently thin that it may be bent in either direction an extentrequired to accommodate the full range of humidity changes withoutcausing undue compression to develop within the hygroscopic facing stripwhen the relative humidity rises to its maximum. Also, the backing stripmust have sufficient rigidity or stiffness and resiliency to give it thestrength and stability necessary for an efficient instrument, and itmust not develop case hardening. internally by reason of being bent ineither direction.

Alaska cedar has been found to possess to a greater extent than anyother wood of which I now have knowledge, those requirements necessaryfor an efficient and durable instrument, and yew wood mostsatisfactorily serves for the facing strips by reason of the fact thatit may be out very thin, may be treated to open its pores withoutdetrimental effect, and is a wood that may be bent back and forth manythousands of times and yet always return to its original position.

Very satisfactory results have been obtained with a backing stripapproximately .044 of an inch in thickness and a facing stripapproximately .024 of an inch thick. This relationship of thickness hasbeen found by experiment to provide an instrument that is sensitive,accurate and which will accommodate the full range of humidity changewithout change in calibration, that is, the backing strip has therequired thickness to give it the strength necessary to providedurability and a high power of restitution, and has the necessarythinness to avoid case hardening within itself or the facing. Also, thefacing strip is sufficiently thick to effectually bend the backing stripeither under compression or tension, yet is of such thinness that itsubstantially instantly responds to the slightest change in humidity.

In the construction of elements of this character, it is desirable tohave as much movement as possible without subjecting either the facingor backing strip to strain beyond its elastic limit. Thus it is requiredthat careful attention should be given to the preparation, especially ofthe hygroscopic facing strip. The extent of contraction and expansion toa definite degree is governed by the direction of grain of the piece,and one of the important features of this invention is the method ofcutting the strips to provide for a definite percentage of expansion.This method is best understood by reference to Figlll'? 6 Of the drawingwherein 20 designates a board of wood from which a strip 21 is to beout. As here shown the board has a certain percentage of expansion inthe crosswise direction. of the grain of the wood and no appreciableexpansion 1n the lengthwise direction, therefore, by cutting the stripin a properly calculated diagonal line, as at 21, a definite percentageof expansion and contraction due to changes of humidity may be providedfor; it being understood that this will vary from approximately zero tothe maximum possible for this strip of wood, in accordance with theangularity of the diagonal cut.

Heretofore, in the construction of instruments of this character, stripsof wood of considerable width have been used, but his results ininaccuracy by reason of transverse cupping of the elements, due tounequal expansion or contraction of the joined strips incident to anyquick change in relative humidity. For instance, if the element isperfectly flat at one certain condition of humidity, and the air shouldsuddenly become very dry, the thin facing strip will shrink rapidly in adirection transversely of the strip, while the backing strip, beingrelatively nonexpansible and non-contractible, will respond slowly.Therefore the unequal stresses set up in the two pieces, which arefirmly glued together, cause transverse cupping, and this increases theeffective thickness of the element and as a natural consequence rendersthe strip more rigid and thereby retards it in its movement. Thisnaturally makes an error in the reading which will be given or otherwiseinterferes with action of the instrument.

In the present instance, this abo 1e difficulty has been satisfactorilyovercome by making up an element from wide strips of material, thensplitting it through both strips into a plurality of relatively narrowstrips. In the present instance these narrow strips are made aboutoneeighth of an inch wide, and they are used in multiples of two aspresently described, to compensate for possible warping. With the stripscut very narrow, transverse cupping will not occur to any extent thatwould cause any noticeable variation from a correct reading.

Devices of this character,- as heretofore made, also become inaccurateby reason of longitudinal twisting. This will be.the result when facingstrips are used in which the direction of the annual rings of the wood,as seen on the surfaces of the facing strips, are not directly acrossthe strips. The use of a facing strip in which the direction of theannual rings is angularly across the strip causes the strip to expand orcontract unevenly thus to twist in a spiral manner lengthwise and theextent of warping is usually in accordance with the degree to which thedirection of the annual ring marks of the material varies from a linedirectly across the strip. In other words, the greater the anglerelative to a direct transverse line, the greater will be the degree ofwarping of the strip. In the present instance I ing the strips in suchmanner that the angular inclination of the ring marks of one strip isopposite to and equal to the inclination of thoseof the strip pairedtherewith. Thus when the original wide strip is split into thin piecesto avoid cupping, every other piece may be turned end for end so thatthey constitute pairs of strips in which the direction of the rings inone will be opposed to that of the other.' That is, the arrangement issuch that the tendency of any one' of the individual strips to warp inone direction a room where the air is very moist.

by reason of the diagonal direction of the ring will be overcome by theuse of a complimentary piece, which is arranged to give an equal warpingtendency in the opposite direction, and the net result is that thestrains balance each other. This arrangement of the pieces is indicatedbest in Figure 2, where the direction of the annual rings is designatedby the shade lines placed thereon. For best results, all facing stripsshould either be tangential or radial cut but exact radial cuts arepreferred.

Another feature of the present invention is the method of compensationwhich results in an instrument of permanent calibration. This isaccomplished by use of the two series of strips in tandem, as shown inFigure 1. The strips of one series would be made up in a dry room. Thestrips of the other series would be made up in The water free cementwould be applied only to the backing strips and allowed to dry somewhatbefore the end grained strips are applied thereto. This precaution inthe gluing results in a minimum penetration of the glue into the endgrained pieces. Then at approximately 30 per cent humidity the stripsmade up in the dry room should be straight, and at approximately 85 percent humidity the strips made up in the moist room should be straight.At 60 per cent humidity the two sets of strips when arranged as inFigure 1 will be bent practically equal amounts, but in oppositedirections. Should the instrument be subjected to eighty per centhumidity, there will be atendency toward case hardening in the stripmade up at the low moisture content. Then if the humidity is changed to50 per cent, this strip will tend to underrun its mark, and the otherstrip will not come quite down to the mark, due to a tendency forinternal lag. Therefore, these two tendencies will approximately balancewhen the two sets of strips are tied together, as illustrated, by use ofthe links 6, thus resulting in a substantially perfect reading.

Having thus described my invention, what I claim as new therein anddesire to secure by Letters Patent is-- 1. In an instrument of thecharacter described, a plurality of co-acting humidity sensitiveelements each including as a part thereof a hygroscopic wooden stripsensitive to humidity changes; the strips of the various elements beingopposedly arranged with respect to their fiber structure, thereby tobalance in the instrument effects of warping tendencies in the indiidual elements.

2. In an instrument of the character described, a plurality of humiditysensitive, co-acting elements in paired relation, each comprising aresilient backing strip and a hygroscopicwooden facing strip securedthereon; the facing strips of paired elements being alike with respectto fiber structure but reversed in position on the backi strips, therebyto effect in the-instrument a balance of warping tendencies.

3. In an instrument of the character described, a plurality of humiditysensitive, co-acting elements in paired relation, each comprising aresilient backing strip and a hygroscopic wooden facing strip securedthereon; the facing strips of paired elements being end grain cutsarranged on their respective backing strips with the .direction ofinclination of annual rings reversed to cause counter action of warpingtendencies.

4. An instrument of the character described comprising humiditysensitive elements arranged r is humidity sensitive elements similarlyarranged and in parallel relation with ends fixed in said support, meansjoining together the other ends of said elements for unitary movement;each of said elements comprising a resilient backing strip and ahygroscopic wooden facing strip secured thereon; the facing strips ofalternate elements being end grain cuts arranged on their respectivebacking strips with the direction of inclination of the annual ringsreversed to effect a balance in warping tendencies.

WORTH C. GOSS.

